Asynchronous Transfer Mode (ATM) switches are connected to each other via Inter-Nodal Links (INLs). In major metro areas, multiple switches are typically connected via a mesh of interconnection, such as a star configuration, or a hierarchical “edge/core” configuration. In most metro locations, the INLs are TDM circuits, and SONET Add/Drop Multiplexers (ADMs) are used to carry these circuits. SONET ADMs are typically arranged in a point-to-point configuration or in rings.
This configuration creates a 2-layer network. The upper layer comprises Asynchronous Transfer Mode (ATM) switches that are connected with each other using Inter-Nodal Links (INLs). The lower layer comprises SONET rings, which contain Add/Drop Multiplexers (ADMs) connected in a point-to-point or ring fashion. The INLs may be routed over the SONET rings without regard to impact of such routing on the survivability of the ATM layer. This can result in single point of failures (SPOFs).
Specifically, for provisioning and routing, multiple Inter-Nodal Link (INL) circuits can be put on the same SONET Add/Drop Multiplexer (ADM) (and even on the same interface card). While SONET provides underlying survivability via Automatic Protection Switching (APS) and diversity rings, the above scenario creates Single Point of Failure (SPOF) for multiple INLs that come from the same Asynchronous Transfer Mode (ATM) switch or set of related ATM switches.
Identifying and analyzing the survivability impact of these Single Points of Failure (SPOF) and providing alternatives to such SPOFs, to increase the overall survivability of the Asynchronous Transfer Mode (ATM) network is a big challenge for network operators.
Currently there are some mechanized tools that identify Single Points of Failure (SPOFs) at the Asynchronous Transfer Mode (ATM) layer based on the Inter-Nodal Link (INL) topology, but without knowledge of the SPOFs in the underlying SONET layer. Similarly, there are tools that identify SPOFs at the SONET layer, but they do not have knowledge of the impact on the upper layers, e.g., ATM layer. SPOFs in a two-layer network (e.g., ATM over SONET) cannot be identified accurately without knowledge of both layers. Further, such tools are not adapted for use with existing SONET inventory systems.
In other words, present Single Point of Failure (SPOF) identification tools lack a comprehensive 2-layer (e.g., Asynchronous Transfer Mode (ATM) & SONET) analysis, and even as a tool in a single layer analysis only operate for “Greenfield” environments where no existing SONET inventory system (such as Trunk Information Record Keeping System (TIRKS)/Planning Work Stations (PWS)) can be easily accommodated. As a result, network designers and planners have difficulty in locating SPOFs using a single tool. This can lead to catastrophic network failures.